APT screw access?

[Goat and Chicken Farmer]

Cliff, I have a 7043202 F3 that was under my bench for the last 30 years or so. I have decided this will be a great carb to exercise my new found knowledge gleaned from your book. I have noticed a few things that I have questions about; like the APT screw access, is this just a disc plug that can be drilled and removed? Also, on inspection, I found the main air bleeds to be the .125 large ones. There is a whole page (112) concerning this but I am a little confused here. The carb had .036 idle tubes, .046 idle down channel, .070 upper idle air bleeds, .070 lower idle air bleeds, 74C main jets, 44B pri. Rods, DA secondary rods with an L hanger, .065 idle mix holes, .111 idle by pass with no hole in throttle plates. I would like to set this carb up to basically bolt on and go, on a stock or mild cam’d Chevy 350 auto trans. Is it necessary to be more application specific or is there a good generic recipe that will make a good performer?  Eventually, I would like to sell it or trade it for a PONTIAC carb, 69 or 71 as we are building 400’s for  the 71 GTO and the 69 Firebird.

[Cliff Ruggles]

Use a sharp punch and poke a small hole in the center of the cap and pry it out with a scripe or awl.

Find or make a screwdriver that fits the APT screw correctly.  Do NOT put much force on the screw, it will snap right off.  Apply some penetrating oil to it, and use some heat from a propane torch to the bottom side of the throttle body. 

Once the casting heats up some about 99 times out of 100, the screw will back right out.

We make an external screw here with a spring on it.....Cliff

[Goat and Chicken Farmer]

Well...of course getting the plug out was no sweat, after reading here I knew I should use penetrating fluid and heat as I did, but the slightest effort and off came one of the tangs on the screw, argh. I have also noticed that the front mounting bolt holes in the air horn showed signs of over-tightening and sure enough both the body and air-horn are pretty warped, it doesn’t appear that the sealing surface (the raised ridge area) on the body has been affected. Should I put on the brakes here and find a better core or can I recover?

[Goat and Chicken Farmer]

What to do now?

[Cliff Ruggles]

The key to removing the early APT screws is to not try to turn the screw without a good fitting screwdriver, and after it's been well soaked with penetrating fluid, and heated up.

Those screws twist of pretty easy, as you found out.

Even doing everything right, there are still a few that just aren't coming out no matter what you do.

Very difficult to drill them out, as they are hardened as well.

Looks like you are down to trying to drill it out, or replacing the throttle body if you want the APT feature.

It's not manditory, as we've been building and tuning early Q-jets for decades successfully for decades that didn't use it.....Cliff

[Goat and Chicken Farmer]

Thank you for responding...I was wondering if I couldn’t just leave that happy ass screw right where it is and still build a good carb. Judging from your response, I can. Besides the fact I cant see anymore, I really didn’t want to open the extraction can of worms, even though I was already thinking of a way to make a pilot that would go into the plug hole to center the small drill bit to drill the stupid screw. Whew! As far a warpage goes, I put a straight edge across the body and it contacts all the raised rib around the body, but the front two corners are about a 1/6th low (didn’t measure yet). The air horn corners are also low. The car that I am building this for is the guy down the street who has a 1967 Chev Malibu 327 .030 over stock rebuild with stock cam, factory exhaust manifolds, duel exhaust, auto trans, stock rear (owner has no clue of rear end ratio or much else for that matter) Pretty clean car but nothing real special HP wise. Anyway, the guy was over saying how crappy quads are but he just cant get it just right with the edlebrock he got to replace it. He would be willing to try the quad that I build and it will make for good practice for me, so what do I need?

[Cliff Ruggles]

We've build hundreds of those carbs without using the APT feature, it's just a nice feature if available, and allows for fine tuning of the part throttle A/F ratio without changing parts.

The carb will work fine for the application.  I would recalibrate it (jets, metering rods and smaller main airbleeds), and install one of our rebuild kits to get it up to par for modern fuels.....Cliff